In an apparatus, for example, receiving analog television signals, analog processing as shown in FIG. 2 has been used in the prior art technology. In more detail with reference to FIG. 2, a high frequency signal supplied to an input terminal 21 is supplied to a first mixer circuit 22 and mixed with a first local oscillation signal from a first local oscillator 23 such that an intermediate frequency signal is formed. The intermediate frequency signal from the first mixer circuit 22 is supplied to a video carrier wave reproducer circuit 24 and a video demodulator circuit 25, and a demodulated video signal is derived at an output terminal 26.
At the same time the intermediate frequency signal from the first mixer circuit 22 is supplied to a second mixer circuit 27 and mixed with a video carrier wave from the video carrier wave reproducer circuit 24. In this way a modulated sound signal of stabilized carrier phase is formed and this modulated sound signal is supplied to a sound demodulator circuit 28 where a demodulated sound signal is derived at an output terminal 29. Accordingly video and sound signals included in the high frequency signal which is supplied to the input terminal 21 are demodulated and derived at the output terminals 26 and 29 respectively.
In view of the above apparatus, the video modulation system of the conventional analog television signals is a suppressed-carrier amplitude modulation system and a video carrier wave is reproduced in the video carrier wave reproducer circuit 24. In this case the signal based on such a suppressed-carrier amplitude modulation system has a tolerable-characteristic merit in phase noises and/or frequency changes, so that it is possible to derive demodulated video signals at the output terminal 26 after demodulating in the video demodulator circuit 25 by using the reproduced video carrier wave.
On the other hand the sound demodulating system of the analog television signals is generally a frequency modulation system which is easily influenced by the phase noises and/or frequency changes. However, in the above mentioned apparatus video carrier wave reproduced in the video carrier wave reproducer circuit 24 is supplied to the second mixer circuit 27 where the phase noises and/or frequency changes are cancelled by the phase noises and/or frequency changes included in that video carrier wave, so that a stabilized signal can be processed.
In this way a stabilized modulated sound signal in which phase noises and/or frequency changes are cancelled is derived from the second mixer circuit 27 and a signal from the second mixer circuit 27 is supplied to a sound demodulator circuit 28. Accordingly a demodulation is performed in the sound demodulator circuit 28 based on a stabilized modulated sound signal in which phase noises and/or frequency changes are cancelled, so that it becomes possible to derive a stabilized sound output signal at an output terminal 29.
On the other hand, recent years a digital type television broadcasting started and digital television receivers which receive digital television signals have begun spreading. In such digital television receivers the reception, the demodulation and the like are all performed by digital processing. However, it should be noted that analog type television broadcasting is also maintained now, so that it is demanded that analog television signals can also be received in such digital television receivers.
For this purpose the conventional digital television receivers are additionally provided with receiving means for receiving analog television signals by means of analog processing as shown in FIG. 2 independently to the receiving means for receiving digital television signals by means of digital processing. However, it should be noted that numbers of parts which constitute circuits increase by providing 2 channels of such receiving means, so that it causes a problem of higher cost and causes a bother for smaller-size's demand, and at the same time it causes a problem of power-consumption increase and the like.
The present invention has been made in view of such conditions, and problems to be solved are directed to that, in the conventional apparatus, receiving means for receiving analog television signals is based on analog processing such that receiving means for receiving digital television signals and for receiving analog television signals should be independently provided where numbers of parts which constitute circuits increase, so that it causes a problem of higher cost and causes a bother for smaller-size's demand, and at the same time it causes a problem of power-consumption increase and the like.